Finite Element Analysis of Customized Acetabular Implant and Bone after Pelvic Tumour Resection throughout the Gait Cycle

The aim of this paper is to investigate and compare the stress distribution of a reconstructed pelvis under different screw forces in a typical walking pattern. Computer-aided design models of the pelvic bones and sacrum made based on computer tomography images and individually designed implants are the basis for creating finite element models, which are imported into ABAQUS software. The screws provide compression loading and bring the implant and pelvic bones together. The sacrum is fixed at the level of the L5 vertebrae. The variants of strength analyses are carried out with four different screw pretension forces. The loads equivalent to the hip joint reaction forces arising during moderate walking are applied to reference points based on the centres of the acetabulum. According to the results of the performed analyses, the optimal and critical values of screw forces are estimated for the current model. The highest stresses among all the models occurred in the screws and implant. As soon as the screw force increases up to the ultimate value, the bone tissue might be locally destroyed. The results prove that the developed implant design with optimal screw pretension forces should have good biomechanical characteristics.

Pelvic discontinuity: a challenge to overcome

Pelvic discontinuity (PD) has been a considerable challenge for the hip revision arthroplasty surgeon. However, not all PDs are the same. Some occur during primary cup insertion, resembling a fresh periprosthetic fracture that separates the superior and inferior portions of the pelvis, while others are chronic as a result of gradual acetabular bone loss due to osteolysis and/or acetabular implant loosening. In the past, ORIF, various types of cages, bone grafts and bone cement were utilized with little success. Today, the biomechanics and biology of PD as well as new diagnostic tools and especially a variety of new implants and techniques are available to hip revision surgeons. Ultraporous cups and augments, cup-cage constructs and custom triflange components have revolutionized the treatment of PD when used in various combinations with ORIF and bone grafts. For chronic PD the cup-cage construct is the most popular method of reconstruction with good medium-term results. Dislocation continues to be the leading cause of failure in all situations, followed by infection. Ultimately, surgeons today have a big enough armamentarium to select the best treatment approach. Case individualization, personal experience and improvisation are the best assets to drive treatment decisions and strategies. Cite this article: EFORT Open Rev 2021;6:459-471. DOI: 10.1302/2058-5241.6.210022

The ethylene oxide sterilised Opera acetabular component demonstrates high rates of loosening and revision compared to the gamma irradiated Ogee cup: a cohort study demonstrating potential shortcomings of revision-based registry data

Aims: To evaluate the long-term clinical outcomes of 2 cemented ultra-high molecular weight polyethylene (UHMWPE) acetabular components, with the main difference between the 2 components being their method of sterilisation. Patients and methods: Data was collected prospectively on 352 consecutive total hip replacements, performed between March 2000 and July 2004, at a single centre. A posterior approach was used with a cemented C-Stem femoral component (DePuy, Warsaw, IN, USA) in all cases and either the Ogee (DePuy, Warsaw, IN, USA) or the Opera (Smith & Nephew, Memphis, TN, USA) acetabular implant. Patients were reviewed clinically and radiologically with a median 12-year follow-up (6–16 years). Results: The risk of experiencing loosening was 90% lower for the Gamma irradiated implant (GII) group compared to the ethylene oxide sterilised implant (EOSI) group, which was statistically significant ( p = 0.003), (HR 0.10; 95% CI, 0.02–0.45). The incidence of cup revision was also lower in the GII group ( p = 0.029), but after adjustment for age, gender and BMI was not statistically significant ( p = 0.104). 15-year survivorship with failure/loosening as an endpoint was 70.1% for the EOS implant and 92.9% for the GII (OR 4.99; CI 95%, 1.75–14.2) and with revision as an endpoint was 81.4% for the EOSI and 92.9% for the GII (OR 2.60; CI 95%, 0.87–7.75) Conclusions: We report increased rates of loosening, revision and failure for the EOSI compared to the GII at long-term follow-up. This may have been attributable to the different sterilisation methods used.

Feasibility And Availability of Standard-Sized Cup At The True Acetabulum In Acetabular Reconstruction of Crowe Type IV Hip Dysplasia

Background: This study aimed to investigate the morphological features and 2D/3D coverage parameters of the true acetabulum of Crowe type IV hips and to identify the optimal component center of standard-sized cup implantation.Methods: A total of 42 Crowe IV hips in 37 patients and 36 normal hips were included in the present study. Based on 3D reconstruction, anatomy and volume of the true acetabulum were measured quantitatively. Through simulated implantation, the feasibility of standard-sized cup implantation was evaluated by cup-based morphological assessments and coverage parameters. Eventually, bony landmarks for optimal component center location were determined. Mean follow-up was 4.7 years (1.2 to 6.3 years).Results: All the dysplastic hips were placed with standard-size acetabular implant (44.67mm, 44 to 48mm) successfully, with no acetabular implant loosening during the follow-up period. Compared with control group, the dysplastic acetabulum was more anteverted and abductive, with a thicker medial wall. According to the true acetabulum, bone stock is relatively sufficient in the posterior direction and prominently deficient in the anterosuperior and superior direction. Average 3D component coverage can reach 79.89% by standard-sized cup implantation at the true acetabulum. Regarding the component opening plane, the optimal component center located at the midpoint between the superolateral and posteroinferior point of the true acetabulum. Conclusion: Standard cup implantation is feasible and available in Crowe IV hip at the true acetabulum. The optimal component center was determined to be relatively constant based on the useful bony landmarks.Level of evidence: Therapeutic Level 3b.

Customised three-dimensional printed revision acetabular implant for large defect after failed triflange revision cup

Aseptic loosening is the most common cause for total hip arthroplasty revision. Acetabular cup revision is a significant challenge in the presence of a large bone defect. One of the options for cup revision in the presence of a large bone defect is the recently introduced customised three-dimensional (3D)-printed reconstruction. We present the case of a 68-year-old woman successfully treated with a customised revision acetabular implant for the failure of triflange cup in the presence of large acetabular defect. The modern orthopaedic surgeon must have full knowledge of customised 3D-printed reconstruction to have as a reserve solution for difficult hip revision surgery.

Single-Stage Revision of an Infected Total Hip Replacement Using Antibiotic-Impregnated Bioabsorbable Beads in a Canine Patient

This report describes a technique and the outcome following surgical revision of a periprosthetic infected total hip replacement (THR) in a single-stage procedure with the use of antibiotic-impregnated bioabsorbable beads. A 6-year-old German Shepherd dog underwent THR 16 months previously, which subsequently became infected. The contaminated femoral and acetabular prostheses were explanted. A femoral window was used to remove the stem and cement. The endosteal surfaces of the femur and acetabulum were reamed to remove periprosthetic tissues. The femoral window was replaced and secured in position with multiple cerclage wires. A 3.5-mm locking plate was applied to the lateral aspect of the femur to prevent fracture of the proximal femoral metaphysis and trochanter. Bioabsorbable beads of calcium sulphate, impregnated with vancomycin and gentamicin, were impacted into the femoral canal followed by an uncemented femoral stem. An uncemented acetabular implant was impacted and additional antibiotic beads placed in the vicinity prior to closure. There has been no evidence of reinfection 5 years postoperatively. Analgesic and antibacterial drugs were not required during this follow-up period; activity is unrestricted with neither lameness nor pain present. Simultaneous revision of both femoral and acetabular periprosthetic infected THR implants was successfully achieved in this patient via a single-stage procedure using uncemented implants and antibiotic-impregnated bioabsorbable beads.

The use of an Ossis custom 3D-printed tri-flanged acetabular implant for major bone loss: minimum 2-year follow-up

Introduction: Custom 3D-printed acetabular implants are a new technology used in hip surgery with ever-increasing frequency. They offer patient-specific implants to optimise filling of bone defects and implant-bone contact, without the need for excessive bone resection. Methods: This is a retrospective cohort study of 46 consecutive patients who underwent an Ossis unilateral custom 3D-printed acetabular implant. Clinical (Oxford Hip Score OHS-60), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Harris Hip Score (HHS) and radiological (restoration of biomechanical hip centre, osteointegration, wear, heterotrophic ossification) results were assessed. Results: Patient mean age was 68 years and follow-up was 38 months (minimum 24 months). 10 patients were excluded from the outcome analysis; 2 patients died, 1 required revision for deep infection and 7 were lost to follow-up. Of the 36 patients included, 21 had severe osteolysis. 7 were revised for infection, 3 for tumoural defects, 3 for metallosis, 1 for dysplasia and 1 for trauma (Paprosky 2a [n=6], 2b [n=2], 2c [n=5], 3a [n=6], 3b [n=11], pelvic dissociation [n=6]). OHS significantly improved postoperatively (16-8-48.4 p=0.027). Postoperative functional scores were good (WOMAC 98; HHS 79). The biomechanical hip centre was restored in all patients. 1 patient had early implant migration with subsequent stabilisation. 2 patients had radiographs concerning for failure of osteointegration. 1 patient had recurrent dislocations. Conclusions: The mid-term results of the Ossis custom 3D-printed tri-flanged acetabular implant for the management of severe acetabular defects are encouraging. The improvement in functional scores and radiographic outcomes are comparable to similar designs. In addition, no cases have required revision for aseptic loosening.